This invention relates to a piston for a hydraulic control apparatus for a clutch, especially for a motor vehicle, comprising at least one emitter or receiver cylinder.
More particularly, the invention relates to a hydraulic control apparatus for a motor vehicle clutch comprising at least one cylinder having a cylinder body with a base portion at the front and open at the rear, a piston mounted for axial sliding movement in an internal bore of the cylinder body, at least one dynamic sealing ring carried by the cylinder body for cooperation with the outer periphery of the piston, a piston rod having at the front a head for cooperation with the piston, of the type in which the cylinder body is of plastics material, and of the type in which the piston delimits a hydraulic chamber axially at the front, and is connected at its rear end with the piston rod.
Such an apparatus is described for example in the document DE-U-295.16.488, or in French patent application No. 98 07213 of Jun. 9, 1998.
In a design which is known for example from French patent application FR 99 02426, the piston of the hydraulic control apparatus is of the type comprising a metallic tubular jacket, especially of aluminium, sheet metal or steel, which is open axially on either side and within which there is mounted, as sealingly as possible, a piston body, especially one of plastics material, in such a way that the assembly consisting of the tubular metal jacket and piston body constitutes a moving part which is movable axially in both directions in the bore of the cylinder body.
The invention aims to propose an improved design for such a piston, which, in particular, enables it to be made as cheaply as possible while improving the axial sealing of the hydraulic chamber, the rear end of which is delimited axially by the piston.
With this in view, the invention proposes a piston of the type mentioned above, characterised in that the jacket includes an internal cross wall which lies in a radial plane and which is formed integrally in one piece with the tubular body of the jacket so as to delimit axially at the front a hydraulic chamber in a cylinder body, in which the piston is mounted for axial sliding movement.
According to other features of the invention:
the jacket is formed by impact drawing;
the cross wall delimits, axially at the front, a rear cavity of the jacket which is open axially towards the rear and which receives the attached piston body;
the piston body is a member made by moulding, especially in plastics material;
the piston body is a member of generally cylindrical form complementary to that of the rear cavity of the jacket into which it is introduced axially forward from the rear, and in which it is immobilised axially in abutment against the facing rear face of the intermediate cross wall;
the piston body is immobilised by a retaining washer mounted in the rear cavity;
the free rear end of the piston body includes means for connecting the piston to the front end of a piston rod;
the free rear end of the piston body is configured as a concave or convex sphere for mounting and articulation on the front end of the piston rod;
the axial thickness of the cross wall is substantially equal to the radial thickness of the jacket;
the axial thickness of the cress wall is substantially greater than the radial thickness of the jacket, and the cross wall is arranged at the front end of the jacket;
the axial passages are formed in the peripheral surface of the jacket in line with the thick cross wall;
the cross wall delimits, axially towards the rear, a front cavity of the jacket which is open axially forward;
the front cavity receives an axial insert, of which a front transverse end face constitutes an engagement surface for the rear axial end of a piston spring;
the front cavity receives the axial rear end of a piston spring in direct axial engagement;
the cross wall is arranged at the longitudinal rear end of the jacket, and it includes, on its rear face, means formed integrally with the cross wall and the jacket, for attaching the piston to the front end of a piston rod;
the said means comprise a sphere for mounting and articulation on the front end of the piston rod.
The invention also proposes the hydraulic control apparatus for a clutch, especially a motor vehicle, characterised in that it includes a piston made in accordance with the features of the invention.
Further features and advantages of the invention will appear on a reading of the following detailed description, for an understanding of which, reference will be made to the attached drawings, in which: